1. Field of the Invention
The present invention relates to a radiotherapy apparatus and more specifically to a radiotherapy apparatus used for stereotactic radiotherapy.
2. Description of the Related Art
A radiotherapy apparatus for treating cancers and tumors using radiation is known. As a 3-dimensional irradiation radiotherapy apparatus which irradiates stereotactic multi-path radiotherapy apparatus, radio-surgery therapy apparatus, lineac (medical linear accelerator) therapy apparatus, and others are known in “Radiotherapy physics”, by Takehiro Nishidai, (Bunkodo, Feb. 26, 2001, pp. 95–153) and “Radiotherapy Manual”, by Masahiro Hiraoka, Keishi Sasai, and Toshihiko Inoue, (Chugai-Igakusha, Apr. 10, 2001, pp. 19–63).
Now, stereotactic multi-path irradiation is radiotherapy to irradiate radiation concentratedly to a small seat of disease from multi-directions to achieve radiotherapy effects, and at the same time, to hold the exposure dose of the surrounding tissues to the minimum. The therapy indicates its greatest force in radiotherapy of primary benign brain tumors, solitary metastatic brain tumors not larger than 3 cm in size, minor lesion in a brain such as skull base metastasis which is difficult to operate, or arterial malformation or venous maloperation, and others.
The radiosurgery therapy apparatus irradiates thin radiation beams to a predetermined small area from one or multiple radiation irradiation units fixed to therapy apparatus. As radiation irradiating units, a gamma ray source or lineac is used. In the radiosurgery therapy apparatus, the diseased part of a patient such as skull or the peripheral regions are mechanically fixed by using a precision positioning/diseased part fixing jig, which is a fixing tool for stereotactic radiation irradiation. This frame is used as a coordinate reference jig for positioning, and diagnostic images are obtained using X-ray CT (computed tomography), MRI, and the like, and the exact position and shape of the diseased part are deduced. The patient is mechanically fixed as-framed to an irradiation apparatus which includes one or multiple radiation irradiation units and a collimater mechanism that collimates and concentrates the therapeutic radiation to a small region. By this, the radiation field is accurately adjusted to the small region mechanically, and precise stereotactic irradiation is carried out. In the radiosurgery therapy apparatus, radiation (X-ray) for radiotherapy is irradiated based on the diagnostic images filmed in advance. That is, a diagnostic X-ray system for observation of the diseased part in real time (X-ray generating unit—image detector) is not provided, and the radiation is never irradiated while observing the diseased part in real time.
In the lineac therapy apparatus, isocentric radiotherapy is carried out by rotating a large-size gantry 360 degrees around an axis parallel to the installation surface. In addition to this, by adding vertical movement, 2-dimensional movement in horizontal planes and rotation in the same horizontal plane of the therapeutic bed, diversified irradiations are enabled. In the lineac therapy apparatus, high-speed position control is not possible. Consequently, real-time follow-up irradiation to a therapeutic field which moves at a high speed as movement due to heart pulses is not possible. In addition, as a monitoring section of a radiation field under irradiation, linacgraphy of transmitted radiation of the therapeutic X-rays is used. Because the therapeutic X-ray provides strong permeability and has many scattering radiations, the picture quality for real-time monitor of the radiation field is not superior. In the lineac therapy apparatus, there is a method for following markers mounted to the diseased part by the diagnostic X-ray system, estimating the position of the diseased part, and irradiating the radiation when the estimated position overlaps the radiation field (body-in-motion tracking irradiation). Now, the diagnostic X-ray system includes a diagnostic X-ray generating unit mounted to the ceiling and an image detector mounted to the lower part of the lineac therapy apparatus. In this method, it is not practiced to grasp the position of the actual diseased part in real-time and to irradiate radiation to it while tracking in such a manner that the actual position of the diseased part overlaps the radiation field. Because the X-ray generating unit is fixed to the ceiling, the distance with the image detector is large. In addition, there is a case that the image detector enters the shadow of a main body of the lineac therapy apparatus, so that the diagnostic X-ray from the X-ray generating unit may not reach the image detector. To cope with it, a slightly larger number of X-ray generating units are mounted to the ceiling, and two usable ones are selected to use. Furthermore, the image detector is installed in the region to which transmission X-ray (the therapeutic X-ray that penetrated the diseased part) and scattering X-ray (the therapeutic X-ray that are scattered in the diseased part) are directed.
In conjunction with the above description, stereotactic surgical apparatuses and methods are disclosed in PCT International Patent Applications (International Application Nos. PCT/US91/07696, and PCT/US93/11872).
One of these stereotactic surgical apparatuses is an apparatus which isocentrically drives electronic therapeutic X-ray lineac, and the electronic lineac is provided to a tip section of a general-purpose industrial robot arm. This apparatus essentially achieves non-isocentric irradiation therapy by free moving capabilities of the robot arm with six degrees of freedom. The exact shape and position of the diseased part are determined by X-ray CT and/or MRI in advance and are inferred by relating them to landmark body tissue such as the skull and the breast and markers embedded in or in the vicinity of the diseased part (e.g., a small-size gold plate embedded in the diseased part). The therapeutic X-ray is precisely irradiated while the stereotactic surgical apparatus monitors the movement of the landmark by the two diagnostic X-ray systems with different visual lines at the time of the therapeutic irradiation, and corrects the sight of the therapeutic X-ray. It takes 1 to 2 seconds to correct the sight and 0.5 to 1 second for irradiation time. Of these two diagnostic X-ray systems, the X-ray generating unit is firmly secured to the ceiling. The image receiver (image detector) that receives the transmitted X-ray is disposed to the lower part of the bed. That is, the X-ray generating unit is located considerably distant from the image detector. In addition, due to the rotation of the lineac therapy apparatus, the image detector enters the shade of the apparatus and diagnostic X-rays from the X-ray generating unit may not reach the image detector. On the other hand, the image receiver is located on the opposite side to the therapeutic X-ray irradiating apparatus with respect to the bed. That is, the image receiver is installed in a region where transmitted X-ray or scattered X-ray are directed.
The other of the above stereotactic surgical apparatuses is an apparatus that drives the electronic lineac along the gantry, and two diagnostic X-ray systems (X-ray generating unit-image receiver) and an electronic lineac are provided to the gantry. By allowing the electronic lineac to rotate not only around one axis in the horizontal direction but also around one axis in the vertical direction, three-dimensional irradiation can be achieved. However, the irradiation system is isocentric. In this stereotactic surgical apparatus, too, the exact shape and position of the diseased part are determined by means such as the X-ray CT are inferred by relating them to the landmark body tissues or the markers embedded in or in the vicinity of the diseased part. The therapeutic beams are precisely irradiated while the stereotactic surgical apparatus monitors the movement of the landmark by using the two diagnostic X-ray systems with different visual lines at the time of the therapeutic irradiation, and corrects the sight of the beam. It takes 1 to 2 seconds for time to correct the sight and 0.5 to 1 second for irradiation time.
These two diagnostic X-ray systems are installed on the gantry to which the electronic lineac is installed. In the same manner, the X-ray generating unit is installed on the gantry on the electronic lineac side distant from the electronic lineac. In addition, the image receiver is located on the gantry on the opposite side of the X-ray generating unit with respect to the diseased part. That is, the image receiver is installed in the region where transmitted or scattering beams are directed.
In general, the diseased part of a patient moves even during radiotherapy. In particular, in a diseased part below the neck, an irradiation subject such as a tumor is constantly moving due to the movements and state of organs such as breathing, heart pulses, vermiculation, and urine volume in a bladder. For example, when the patient lies down only, the body gradually becomes flat. In addition, though breathing and heart pulses are cyclic movements, movements of organs associated with them do not always pass the same route every time.
The movement of the irradiated subject is intended to be accurately caught in real time, and the heart pulse, which is one of the quickest movements, is 1 to 2 times/sec. Consequently, in order to obtain accurate tracking of the movement in real time, it is said that a technique to obtain diagnostic images at about 30 images per second is required. If the irradiated subject is accurately tracked in real time and radiation is irradiated, it is necessary to direct the radiation irradiating head accurately to the irradiated subject every 1/30 second. In addition, in order to obtain a high-quality diagnostic image for tracking, it is important to eliminate the effect of the therapeutic radiation (X-rays) to the image detector of the diagnostic X-ray system.